Apparatus for testing circuit boards

ABSTRACT

Apparatus for electrically testing a connector includes a plurality of contact posts (i.e., connector pins) partially surrounded by a sidewall defining an opening adjacent ends of the posts. In one embodiment a translator fixture is interfaced with a plurality of test probes. The translator fixture has a plurality of spaced apart translator plates and holes aligned in the plates for containing and supporting translator pins extending through the plates for positioning the translator pins for direct contact with and engagement by conductive pins of a guide block assembly mounted on the outermost one of the translator plates. The conductive pins are slidably mounted in the guide block assembly. The conductive pins extend from the guide block assembly so as to directly contact, be substantially coaxial with, and engage the distal ends of the contact posts.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the testing of printed circuit boards.The invention has particular utility in connection with determined testfixtures of the type having test probes on a grid pattern, in which atranslator pin fixture is used for translating electrical current froman off-grid pattern on a board under test to the channels of a tester inwhich the channel contacts are arranged in a grid pattern, and will bedescribed in connection with such utility, although other utilities arecontemplated. An especially particular utility for the present inventionis found in the area of facilitating electrical testing of electricalconnectors mounted on a circuit board (commonly referred to as "backplane" or "mid-plane"). These connectors typically are surrounded by asidewall extending beyond the ends of the electrical contact posts.

2. Brief Description of Related Prior Art

Automatic test equipment for checking printed circuit boards has longinvolved the use of "bed of nails" test fixtures on which the circuitboard is mounted during testing. A typical test fixture includes a largenumber of nail-like test probes arranged to make electrical contactbetween spring loaded contacts in the test equipment and designated testpoints on the circuit board under test, also referred to as the unitunder test or "UUT". Any particular circuit laid out on a printedcircuit board is likely to be different from other circuits, andconsequently, arrangement of test probes for contacting test points onthe board must be customized in a test fixture for that particularcircuit board. Board design and fabrication data is used to determinewhat specific board features are to be tested by the fixture. A"determined" grid test fixture is typically fabricated by drillingpatterns of holes in several rigid and non-conducting plates, e.g. ofLexan®, assembling those plates with suitable fasteners and spacers tomaintain said plates in a parallel, aligned position and then mountingtest pins or probes in the drilled holes. Each plate has a hole patternwhich is unique such that the test pin can only be inserted to providean xy and z translation between a unique feature on the UUT and a uniquetester grid channel. The circuit board is then positioned in the fixtureprecisely aligned with the array of test probes. During testing, thepins in the fixture are brought into spring-pressure contact with thetest points on the circuit board under test. Electrical test signals arethen transferred between the board and the tester through the fixture sothat a high speed electronic test analyzer which detects continuity orlack of continuity between various test points in the circuits on theboard can perform the actual test.

Various approaches have been used in the past for bringing the testprobes and the circuit board under test into pressure contact fortesting. One class of these fixtures is a "wired" test fixture or a"dedicated" test fixture in which the test probes are individually wiredto separate interface contacts for use in transmitting test signals fromthe probes to the external electronically controlled test analyzer.These wired test fixtures are often referred to as "vacuum testfixtures" since a vacuum is applied to the interior of the test fixturehousing during testing to compress the circuit board into contact withthe test probes. Customized wired test fixtures of similar constructionalso can be made by using mechanical means other than vacuum to applythe spring force necessary for compressing the board into contact withthe probes during testing.

A further class of test fixtures is the so-called "grid-type fixture"test fixture, also known as a "determined" fixture, in which the randompattern of test points on the board are contacted by translator pinswhich transfer test signals to spring loaded interface pins arranged ina grid pattern in the tester. In these grid-type testers, fixturing isgenerally less complex and can be produced at lower cost than in thecustomized wired test fixtures; but with a grid system, the gridinterfaces and test electronics are substantially more complex andcostly.

A typical tester may have thousands of switches and channels. Eachchannel may have several switches, and is addressable and serves as onecoordinate in the "grid". The tester has spring-loaded contacts whichcomprise the grid. The fixture contains rigid translator pins whichconduct current from the grid channels to the UUT. In this way, thetester's computer can be made to test continuity and isolation in theUUT through the fixture. When testing a bare board on such a tester, atranslator fixture supports and guides rigid pins that conduct between agrid pattern of spring-loaded probes in a grid base and an off-gridpattern of test points on the board under test. In one prior art gridfixture so-called "tilt pins" are used as the translator pins. The tiltpins are straight solid pins mounted in corresponding pre-drilled holesin translator plates which are part of the translator fixture. The tiltpins can tilt in various orientations to translate separate test signalsfrom the off-grid random pattern of test points on the board to the gridpattern of test probes in the grid base.

Further details of prior art fixtures are found, for example, in U.S.Pat. No. 5,493,230 and U.S. Pat. No. 4,721,908.

It has been found that prior art testing apparatus of the typesdiscussed above are not well suited for testing of contact posts mountedin connectors having sidewalls which extend beyond the ends of thecontact posts. As a result, it often proved difficult to achieve good,stable electrical connection between the contact posts and thetranslator pins using prior art fixtures. Additionally, due to thetilting required to make contact to the uniform grid of the tester, thetranslator pins are rarely coaxial with the contact posts when theycontact the posts. Since the contact posts usually are spaced very closetogether in the connector, this can cause translator pins toinadvertently become electrically connected to the wrong contact posts,and/or to each other. These can result in erroneous test results, damageto the circuit board, and/or damage to the testing apparatus. Moreover,with prior art fixtures, it was necessary to drill numerous layers ofLexan® to support and guide the rigid test probes to the level of thecontact tips. Additionally, it was necessary to provide clearance slotson either side of the drilled holes for the connector side walls. Whilesuch techniques were able somewhat to reduce the risk of occurrences ofinadvertent connection of translator pins to wrong contact posts, eachother, and the sidewalls of the connectors, such drilling compromisedthe rigidity of the structure laterally, and often resulted in falseopens and shorts during the testing process. Additionally, suchtechniques added to costs.

It is therefore an object of the present invention to provide a systemfor use in testing of printed circuit boards which overcomes theaforesaid and other objects of the present invention.

A more specific object of the invention is to provide an improvedfixture and guide block assembly particularly for testing contact postsmounted in connectors having side walls that extend beyond the tips ofthe contact posts.

SUMMARY OF THE INVENTION

In accordance with the present invention, a system is provided forelectrically testing a connector having contact posts (i.e., connectorpins) partially surrounded by a sidewall defining an opening adjacentthe tips or ends of the posts. In one embodiment the present inventioncomprises a test fixture having a plurality of spaced apart translatorplates and having holes aligned in the plates for containing andsupporting translator pins in a grid pattern. A guide block assemblycomprising a plurality of slidably mounted conductive pins is located onthe top plate of the test fixture, with the tips or ends of itsconductive pins aligned with the tips or ends of the translator pins ofthe fixture. The guide block is fixedly located on the test fixture bymechanical means such as by posts which are press-fitted into matingholes in the top plate of the fixture.

In a preferred embodiment of the invention, the guide block conductivepins are of one-piece, and the opposite ends of which terminate inconcave shapes for mating with the tips of the fixture translator pinsand with the tips of the contact pins, respectively.

Advantageously, the present invention overcomes the aforesaid and otherdisadvantages and drawbacks associated with the prior art. For example,since in the present invention the guide block conductive pins engagethe translator pins and contact posts, and are generally coaxiallyaligned with the contact posts, better and more stable electricalcontact may be maintained between the translator pins and contact poststhan is possible in the prior art. Additionally, the present inventionsubstantially eliminates the risk of inadvertent connection oftranslator pins to wrong contact posts, each other, and the sidewalls ofthe connectors. Further advantageously, the present invention eliminatesthe need to use the translator pin routing and guiding structures of theprior art, thereby eliminating the expense and time associated withconstruction and utilization of such structures.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention willbecome apparent as the following Detailed Description proceeds and uponreference to the Drawings, wherein like numerals depict like parts, andwherein:

FIG. 1 is a schematic cross-sectional view of a preferred embodiment ofa guide block/test fixture system in accordance with the presentinvention;

FIG. 2 is a top elevational view of the guide block element of thepreferred embodiment of FIG. 1, and in which view the conductive pins ofthe guide block have been removed for clarity;

FIG. 3 is a top elevational view similar to FIG. 2, and showing theinclusion of conductive pins in the guide block element;

FIG. 4 is a side elevational view of one conductive pin of the guideblock element of the preferred embodiment of FIG. 1;

FIG. 5 is a bottom plan view of the guide block element of FIG. 3; and

FIG. 6 is an enlargement of a portion of the schematic diagram of FIG.1.

Although the following Detailed Description will proceed with referencebeing made to a specific embodiment of the present invention, it shouldbe understood that the present invention is not intended to be limitedto this embodiment. Rather, many alternatives, modifications, andvariations thereof will be apparent to those skilled in the art.Accordingly, the present invention should be viewed broadly, as beinglimited only as set forth in the hereinafter appended claims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring to FIGS. 1-6, preferred embodiment 14 of the system of thepresent invention includes a grid base 10 having an array ofspring-loaded test probes 12 arranged on a two-dimensional grid pattern.The test probes illustrated schematically in FIG. 1 preferably comprisean orthogonal array of uniformly spaced-apart rows and columns of testprobes which may be aligned on 100 mil centers as an example. Thespring-loaded plungers of the test probes 12 may project above or liejust below the top surface of the grid base uniformly across the arrayof probes. A translator fixture 15 supports a conventional printedcircuit board 16 under test (also referred to as a "unit under test" or"UUT") having a back plane connector 52 mounted thereon. As will bedescribed more fully below, the translator fixture 15 serves as aninterface between the posts 56 of the connector 52 of the board 16 undertest and the test probes 12 in the grid base 10. An external electronictest analyzer 20 is electrically connected to the posts 56 of the boardunder test through test probes 22 (of which there may be several types)in the translator fixture 15 which in turn is connected to grid base 10,the translator fixture, and the guide block assembly 50, in a mannerthat will be described more fully below.

Connector 52 comprises a plurality of electrically conductive elongatecontact posts (collectively referred to by numeral 56) mounted to oneside 68 of the board 16 and may be connected to various components (notshown) of the board 16 by e.g. conductive traces (not shown). Posts 56extend normally from the surface 68 toward the outermost translatorplate 26 of the translator fixture 15, and are partially surrounded by ashield sidewall 54 which is mounted to the side 68 of the board 16 towhich the posts 56 are mounted. Sidewall 54 typically consists of amolded plastic insulator ground shield which defines an opening 120adjacent the outer rows of posts 56, and extends from the surface 68 ofthe board 16 to a point beyond the distal ends of the posts 56.

The test analyzer 20 contains electronic interrogation circuits toelectronically interrogate (stimulate) the posts 56 of the connector 52of the board 16 under test in order to determine whether the board 16and/or connector 52 are operating properly. The electrical responsesignals produced as a result of such interrogation are compared tostored reference results obtained from simulation of board responseand/or testing of a faultless master board or from an electronicdatabase known as a "netlink." If the response signals and referenceresults match, it is assumed that the UUT and/or connector 52 are good.

Electronic interrogation circuits in this embodiment may comprise aplurality of printed circuit cards (sometimes called "switch cards")having electronic components and printed circuits for carrying out theelectronic testing. Each test probe used in the test procedure isrepresented as being coupled to the test electronics through acorresponding switch 24 leading to the analyzer 20. It should beunderstood that although only six such switches 24 are shown in FIG. 1,any number of switches may be used without departing from thisembodiment of the present invention, depending upon the number of posts56 and other testing points of the board 16 under test.

Translator fixture 15 includes a series of vertically spaced-apart andparallel translator plates 26, 28, 30, 32, which may include a top(outermost) plate 26, an upper plate 28 spaced a short distance belowthe top plate 26, one or more intermediate plates 30, and a grid facingplate 32 at the bottom of the translator fixture. The translator platesare supported in parallel, vertically spaced apart positions by rigidposts 70 that hold the fixture 15 together as a rigid unit. The fixture15 also includes an array of standard translator pins such as tilt pinsrepresented schematically at 22 extending through holes (not shown) inthe translator plates. FIG. 1 represents only six translator pins forsimplicity, but it should be understood that any number of suchtranslator pins 22 may be used depending upon the number of posts 56 andother contact points (not shown) to be tested on the board 16. The tiltpins extending through the base plate 32 of the fixture 15 are inalignment with the grid pattern of test probes 12 in the grid base 10.The top portions of the tilt pins, which extend through the outermostplate 26, are for contacting and being engaged by desired ones of theconductive pins (collectively referred to by numeral 60) of the guideblock assembly 50. Preferably, the tilt pins 22 are straight, solidconductive pins, and extend through a pin retaining means 34.Preferably, retaining means comprises a plastic screen of the typedisclosed in the copending application Ser. No. 08/662,671, entitled,"Retention Of Test Probes In Translator Fixture," filed on Jun. 14,1996, and assigned to the Assignee of the instant application (whichcopending application is incorporated herein by reference), although ifembodiment 14 is appropriately modified, other types of translator pinretaining means may be used without departing from the presentinvention. As disclosed in said copending application, the plasticscreen retaining means 34 preferably is located between the lower mostplates 30, 32 of the translator fixture 15, and includes a multiplicityof interstitial openings which provide for penetration for thetranslator pins 22. The plastic properties of said plastic screenretaining means 34 apply a partial compression force around thecircumference of the translator pins 22 sufficient to retain thetranslator pins within the test fixture 15.

Completing the system of the present invention is a guide block 50 whichis positioned directly beneath the distal ends of the posts 56 andwhich, in preferred form, comprises a rectangular, molded or machinedplastic block 76 having a top surface plan 80 which is undersizedcompared to the opening 120 of the connector 52. Thus, the guide blockis dimensioned to be inserted within the opening 120 so as to permit thesurface 80 to be spaced close enough to the posts 56 to permit the pins60 to contact and engage the distal ends of the posts 56 when pins 60are extended, at least in part to the "up" position, i.e. as shown inFIG. 6. Block 76 also includes integrally formed rectangular legs 72,74, 82, 104, which legs 72, 74, 82, 104 include respective cylindricalportions 90, 92, 94, 106 for mounting into matching holes (shown inphantom at 107) formed in the outermost plate 26 of the fixture toremovably affix the guide block 76 to the outermost plate 26. As seen inFIGS. 2 and 5, legs 72, 74, 82, 104 are staggered so as to permit theguide blocks to be mounted close to one another.

A plurality of cylindrical, electrically conductive pins 60 (comprisingan electrically conductive, machinable metal, e.g. gold platedberyllium-copper or half-hard brass) are slideably mounted in respectivecylindrical holes (collectively referred to by numeral 96). Preferably,pins 60 are longer than the holes 96 by about 150-170 mils , and each ofthe pins 60 comprises opposing top 62 and bottom 64 ends which areslightly oversized compared to the holes 96 and central portions 102in-between the ends 62 and 64, so as to permit the pins 60 to slide inthe holes 96 while preventing them from falling out of the holes 96.Preferably, in this embodiment, pins 60 comprise one piece pins, theends 62, 64 have maximum diameters of 1.524 mm, while the centralportions 102 have diameters of 1.372 mm. Preferably, but notnecessarily, ends 62, 64 are tapered to 1.372 mm. Pins 60 are loadedinto the block 76 by force fitting. Alternatively, pins 60 may comprisetwo piece pins in which case, the pins may be loaded into the block 76from opposite sides, and then mated together. Each of the pins 60 alsocomprises top 98 and bottom 109 concavities (i.e., concave surfaces).Concavities 98, 109 are adapted (i.e., have appropriate dimensions andshapes) to engage and mate with the distal ends of the contact posts 56and the top portions of the translator pins 22, respectively. Also,preferably, the number and configuration of pins 60 match the number andconfiguration of the posts 56 desired to be tested by the apparatus. Thedimensions, shapes, orientations, configuration and pin count of theguide block assembly may be varied, i.e. to accommodate differentconnectors to be tested.

In use, the guide assembly 50 is press fitted, in position, on the topplate 26 of the test fixture. The board to be tested is then positionedin the tester, adjacent the testing fixture. The top portions of thetranslator pins 22 contact with and engage the bottom concavities 109 ofthe conductive pins 60. Compressive force is applied to the pins 60 bythe spring-loaded probes 12 via the translator pins 22 which causes thepins 60 to slide upwardly in the holes 96 such that the top portions 62of the pins 60 extend about 150-170 mils above the top surface portion80 of the guide assembly 76 positioned inside the opening 120 of theconnector 52, and concavities 98 of the pins 60 contact and engage thedistal ends of the contact posts 56. When in contact with the posts 56,each of the pins 60 is substantially coaxial with and mates with arespective one of the contact posts 56. Electrical test signals andresponses may then be transmitted between the contact posts 56 and theanalyzer 20 via the switches 24, test probes 12, translator pins 22, andguide block pins 60 of the apparatus.

Thus, it is evident that there has been provided in accordance with thepresent invention a connector testing apparatus that fully satisfiesboth the aims and objectives hereinbefore set forth. It should beappreciated that although the present invention has been described inconnection with preferred embodiments thereof, many modifications,alternatives, and variations will be apparent to those skilled in theart. For example, although embodiment 14 has been described ascomprising specific types of test fixtures (i.e., test analyzer 20,switches 24, grid base 10, and translator fixture 15 comprising aplurality of spaced apart translator plates), if appropriately modified,embodiment 14 may utilize other types and configurations of testfixtures without departing from the present invention.

Other modifications are also possible. For example, although guide blockpins 60 have been described as all having the same lengths anddiameters, if posts 56 have different lengths from each other, theapparatus may be modified such that pins 60 have different lengths fromeach other so as to permit pins 60 to contact and engage the distal endsof the posts 56 when force is applied to the pins 60 by the translatorpins 22 in the manner discussed previously. The invention alsoadvantageously may be employed in connection with testing of otherprefigured components and/or for in-circuit testing.

Further modifications are also possible. Thus, the present inventionshould not be viewed as being limited to only the specific embodimentsand methods of use hereinbefore set forth, but rather, should be viewedas being of broad scope as only defined as set forth in the hereinafterappended claims.

What is claimed is:
 1. Apparatus for use with a test fixture in testingan electrical connector on a circuit board, said apparatus having aplurality of contact posts partially surrounded by a sidewall definingan opening adjacent ends of said posts, and comprising a translatorfixture having a plurality of spaced apart translator plates forcontaining and supporting translator pins extending through the platesof said translator fixture and positioning the translator pins so as tobe directly contacted and engaged by conductive pins of a guide blockassembly spaced apart from an outermost one of said translator plates,said conductive pins being slidably mounted in said guide blockassembly, and wherein said conductive pins extend from a surface of saidguide block assembly that is undersized compared to said opening so asto directly contact, be substantially coaxial with, and engage distalends of said contact posts via said opening when said connector isoperatively disposed adjacent said test fixture.
 2. Apparatus accordingto claim 1, wherein said conductive pins are slidably mounted in holesformed in said guide block assembly that are (a) oversized relative tocentral portions of said conductive pins, but are (b) undersizedrelative to end portions of said conductive pins.
 3. Apparatus accordingto claim 1, wherein each of said conductive pins has two opposite ends,one of said ends having a concavity to mate with a respective one ofsaid translator pins, the other of said ends having a concavity to matewith a respective one of said contact pins.
 4. Apparatus according toclaim 1, wherein said sidewall extends beyond the ends of saidconductive pins, and said guide block assembly is adapted to bepartially inserted into said opening of said sidewall so as to bepartially surrounded by said sidewall.
 5. Apparatus according to claim1, wherein said guide block assembly is removably mounted to saidoutermost translator plate.
 6. Apparatus according to claim 1, whereinsaid conductive pins are substantially perpendicular to said translatorplates and guide block assembly.
 7. Apparatus according to claim 1,wherein said guide block assembly is made of molded or machined plastic.8. Apparatus according to claim 1, wherein said conductive pins havediameters that are larger than diameters of said contact posts, andsufficient distance exists between said conductive pins when saidconductive pins are in contact with said contact posts to preventshorting of the conductive pins to each other.
 9. Apparatus according toclaim 1, wherein said connector is mounted to a circuit board, and saidapparatus further comprises a support for holding the circuit board suchthat each of the conductive pins is positioned opposite to and coaxialwith a respective one said contact posts.
 10. Apparatus according toclaim 1, wherein the ends of the conductive pins are tapered. 11.Apparatus for facilitating electrical testing of a circuit component,said apparatus having a plurality of contact posts having distal endspartially surrounded by a sidewall defining an opening adjacent ends ofsaid contact posts, said sidewall extending beyond said ends of saidcontact posts, and comprising a guide block assembly removably mountedto and spaced apart from an outermost translator plate of a translatorfixture, said guide block assembly including conductive pins forcontacting translator pins extending through said translator fixture andat least partially into said opening, said conductive pins beingslidably mounted in said guide block assembly, whereby said conductivepins engage both the distal ends of said contact posts and saidtranslator pins when said guide block assembly is at least partiallyinserted into said opening when said connector is operatively disposedadjacent said fixture.
 12. Apparatus according to claim 11, wherein saidconductive pins are slidably mounted in said guide block assembly, anddirectly contact and engage the distal ends of said contact posts whencompressive force is applied to said conductive pins by said translatorpins.
 13. Apparatus according to claim 11, wherein said conductive pinshave a plan configuration that is identical to the plan configuration ofsaid contact posts.
 14. Apparatus according to claim 11, wherein saidconductive pins are substantially coaxial with said contact posts whensaid conductive pins contact and engage the distal ends of said contactposts.
 15. Apparatus according to claim 11, wherein said conductive pinsare mounted in holes in said guide assembly, and each of said conductivepins is of one-piece construction, has two ends that are oversizedrelative to said holes, and a portion in-between said two ends that isundersized relative to said holes.
 16. Apparatus according to claim 11,wherein the ends of the conductive pins are tapered.